An optical wavelength converter is an optical transducer that converts a light having a first wavelength into a color light having a second wavelength. Generally, the optical wavelength converter is applied to a spotlight, a car headlight, a monitor, a projector or other special illumination circumstances.
Conventionally, the optical wavelength converter has a phosphor wheel. When a laser light source emits a laser beam to excite a phosphor powder of the phosphor wheel, a color light with a different wavelength is produced. Moreover, as the phosphor wheel is driven to rotate by a motor, different color lights are sequentially produced according to a time sequence. During the high-power operation, the wavelength conversion efficiency of the phosphor wheel is enhanced, and the photoelectric conversion and the lumen output are increased. Consequently, the optical wavelength converter is used in the light source of the new generation projector in recent years.
FIG. 1A schematically illustrates the structure of a conventional optical wavelength converter. As shown in FIG. 1A, the conventional optical wavelength converter 1 is driven by a motor 2. A phosphor powder 4 is coated on a segment 30 of a substrate 3 of the conventional optical wavelength converter 1. Depending on the type of the substrate, the conventional optical wavelength converters are classified into a transmission-type optical wavelength converter and a reflection-type optical wavelength converter. FIG. 1B schematically illustrates the optical path of a conventional transmission-type optical wavelength converter. FIG. 1C schematically illustrates the optical path of a conventional reflection-type optical wavelength converter. As shown in FIG. 1B, the substrate 3 of the conventional transmission-type optical wavelength converter 1 is a glass plate. An incident light I1 is directly transmitted through the substrate 3 to excite the phosphor powder 4. Consequently, a color light O1 is produced. In this situation, the propagation direction of the incident light I1 and the propagation direction of the color light O1 are identical. As shown in FIG. 1C, the substrate 3 of the conventional reflection-type optical wavelength converter 1 is a glass mirror, a glossy aluminum plate or any other appropriate high-reflectivity plate. After the phosphor powder 4 is excited by an incident light I2, a color light O2 is reflected by the substrate 3. In this situation, the propagation direction of the incident light I2 and the propagation direction of the color light O2 are opposed to each other.
However, with the increasing demands on the luminance of the projector, the optical power of the laser light for exciting the phosphor powder is high. Consequently, the substrate of the conventional transmission-type optical wavelength converter is very hot. Under this circumstance, the wavelength conversion efficiency of the phosphor powder is reduced, and thus the overall output light is adversely affected. Due to these reasons, the reflection-type optical wavelength converter is the mainstream product in the market.
Nowadays, the cooperation of the blue laser beam and the reflection-type optical wavelength converter may be applied to the projector to produce various color lights. FIG. 2 schematically illustrates a conventional optical wavelength converter with a hollow portion. The optical wavelength converter 1 of FIG. 2 is applied to illumination system with a blue laser light source. The blue laser light source may emit a blue laser light. As shown in FIG. 2, the substrate 3 of the optical wavelength converter 1 has a hollow portion 31 for allowing the blue laser light to go through. By changing the area of the hollow portion 31, the proportion of the output blue light is adjustable. However, since the rotation of the optical wavelength converter 1 is driven by the motor 2, it is difficult to control the oscillation amount of the motor 2 under high rotation rate. In case that the diameter of the substrate 3 is larger, the unmatching between the blue laser speckle and the hollow portion 31 is increased, and the rotation of the optical wavelength converter 1 is more unbalanced. Under this circumstance, the intensity and the chroma of the output light are not stable, and the quality of the output light is deteriorated.
Therefore, there is a need of providing an optical wavelength converter for providing a stable and high-quality light source and providing an illumination system with the optical wavelength converter in order to overcome the above drawbacks.